In the oil well drilling and production industry, viscous fluids or gels are often pumped into a well to initiate and propagate underground fractures in order to increase the productivity of the well. Such operations are commonly referred to as well fracturing operations.
The most common method currently used for the continuous on-site preparation of well fracturing gels involves combining a polymeric material with a carrier fluid, such as a hydrocarbon material, in a feeder to form an aqueous solution of the polymeric material. The aqueous solution is then discharged from the feeder and combined with another substance to form a gel. Such a gel preparation method is desirable in that the amount of the aqueous solution that is discharged from the feeder can be precisely controlled, and therefore the resultant gel and its properties can be precisely controlled as well. A drawback of this gel preparation method is that the use of the hydrocarbon carrier fluid, which in many cases is diesel, causes environmental concerns.
Therefore, it is desirable to eliminate the carrier fluid in the feeder, and feed a dry mix of polymeric material from the feeder. However, the flow properties of a dry mix are much less predictable than that of an aqueous solution. This is due to variations in the packing or compactness of the dry mix, the moisture content of the dry mix, and/or the amount of the dry mix in the feeder, among other variations in the environment of the dry mix or other variations in the dry mix itself.
Existing system for discharging a dry mix of a polymeric material from a feeder to form a fracturing gel are described in U.S. Pat. Nos. 5,426,137 and 5,382,411 to Allen; and U.S. Pat. No. 5,190,374 to Harms. These systems include a metering screw or an auger that needs to be calibrated for each dry mix of material that it discharges. However, after the initial calibration of the discharge device, these systems do not include any quality control during the process of discharging the polymer. As such, the actual amount of dry mix that is discharged from the feeder is not measured or controlled.
Instead, the precision and reliability of these systems is dependent solely on the repeatability of the screw/auger to deliver the same amount of dry mix for each turn of the screw/auger. Therefore, using these methods, variations in the flow properties of the dry mix are not taken into consideration. As a result, the properties of the resultant gel that is produced from the dry mix cannot be precisely controlled. Accordingly, a need exists for a method of precisely controlling an amount of a dry mix of material that is discharged from a feeder.